Crystal Structure by ajizai

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									Crystal Structure

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The structure

• The expression of a mineral’s
  internal arrangement of atoms
• The structures of crystals
  depend on
 • the types of bonds between the
   atoms and the conditions under
   which the crystals are formed
Structure




        The cubic shape of salt crystals
        results from the regular
        arrangement of atoms forming the
        crystal.
Importance of structure

• Gives minerals their properties
• Graphite C sheets
• Diamond strongly bonded to 3 other C
  atoms
What shows us the
shape?
• X-rays
• Strike a photographic plate
• Shows arrangement of ions or
  atoms that make up crystal
crystals

• 7 types of crystals



       ISOMETRIC    HEXAGONAL

       TETRAGONAL   ORTHORHOMBIC
                                   Trigonal

       MONOCLINIC    TRICLINIC
Properties of Minerals:
Crystal Structure
• Isometric Group of Crystals
  • “equal measure”
Isometric

• 90*
• Blocky or ball-like
isometric
Mineral Identification
Basics
 • ISOMETRIC           BASIC CRYSTAL SHAPES




           Spinel               Fluorite             Pyrite

   Octahedron               Cube             Cube with
                                            Pyritohedron
                                             Striations



        Garnet      Garnet - Dodecahedron
Trapezohedron
Hexagonal

            120*
            Three horizontal axes
            meeting at angles of
            120o and one
            perpendicular axis.
Mineral Identification
Basics
    • HEXAGONAL   CRYSTALS




                       These hexagonal
                       CALCITE crystals
                       nicely show the six
                       sided prisms as well as
                       the basal pinacoid.
Mineral Identification
Basics
           • HEXAGONAL          CRYSTALS
                 Pyramid
                  Faces                     Pyramid
Prism                                        Face
Faces

                                             Prism
                                             Faces



                     Dolomite
                                     Rhodochrosite
        RHOMBOHEDRON
                                   SCALENOHEDRON
            Vanadinite
            Hanksite
                                   Quartz
Mineral Identification
Basics
    • TETRAGONAL CRYSTALS
                      TETRAGONAL
        c
                      Two equal, horizontal, mutually
                      perpendicular axes (a1, a2)
                       Vertical axis (c) is perpendicular to the
                      horizontal axes and is of a different
             a2       length.
  a1
                                    c


 TETRAGONAL Crystal                             a2
                              a1
       Axes

                           This is an Alternative
                               Crystal Axes
Mineral Identification Basics
     • TETRAGONAL   CRYSTALS




        WULFENITE

                    Same crystal seen edge on.
Orthorhombic

       c                                    c

                                                              b
            b                           a
   a
                                An Alternative Crystal
                                  Axes Orientation

 ORTHORHMOBIC     Three mutually perpendicular axes of different lengths.
   Crystal Axes
ORTHORHOMBIC

          • not square in
            cross section
            (when viewing the
            crystal on end),



             Topaz from Topaz Mountain,
             Utah.
Mineral Identification
Basics
      • ORTHORHOMBIC              CRYSTALS

                   ORTHORHOMBIC
                   This model shows the alternative axes
                   where the vertical “c” axis is not the
                   longest axis.
                   The model shows the outside “brick”
                   shape of the PRISM and the inner shape is
                   a DIPYRAMID. The top and bottom faces
                   are called PINACOIDS and are
 ORTHORHMOBIC      perpendicular to the “c” axis.
   Crystal Model
Orthorhombic




          BARITE is also orthorhombic.
          The view above is looking down
          the “c” axis of the crystal.
Mineral Identification
Basics
     • MONOCLINIC CRYSTALS



          c
                      MONOCLINIC
                      In this crystal form the axes are of
                b     unequal length.
                      Axes A and B are perpendicular.
      a
                      Axes B and C are perpendicular.
 MONOCLINIC Crystal   But A and C make some oblique
      Axes            angle and with each other.
Mineral Identification
Basics
     • MONOCLINIC CRYSTALS




    Gypsum                   Mica
     Orthoclase


                  Top View
Triclinic

                    all axes are of different
                    lengths
      c             none are perpendicular

                    Crystals that form intersect
                    at oblique angles.

              b     no symmetry and no
          a         mirrored planes.


TRICLINIC Crystal
     Axes
Mineral Identification
Basics TRICLINIC CRYSTALS
     •




              Microcline, variety Amazonite
   Crystal Systems
• cubic - not always cube shaped! You'll also find octahedrons
  (eight faces) and dodecahedrons (10 faces).
• hexagonal - six-sided prisms. When you look at the crystal on-
  end, the cross section is a hexagon
• tetragonal - similar to cubic crystals, but longer along one axis
  than the other, forming double pyramids and prisms
• trigonal - possess a single 3-fold axis of rotation instead of the 6-
  fold axis of the hexagonal division
• orthorhombic - like tetragonal crystals except not square in cross
  section (when viewing the crystal on end), forming rhombic
  prisms or dipyramids (two pyramids stuck together)
• monoclinic - like skewed tetragonal crystals, often forming
  prisms and double pyramids
• triclinic - usually not symmetrical from one side to the other,
  which can lead to some fairly strange shapes
                                  Topaz
                      Wulfenite                      Kyanite
Flourite                          Olivine
                      Zircon                         Turquoise
Halite                            Sulfur
diamond                           Chrysoberyl        Axinite




           Emerald                          Gypsum
           Graphite                         Mica
           Apatite

								
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